Method and apparatus for producing turbine blade roots

Abstract

A method and apparatus for producing turbine blade roots (23) utilize an electro-discharge machining apparatus (10) to machine critical portions of the blade root (23) and a peening apparatus (25) for peening of the machined portions. The electro-discharge machining of the blade root leaves recast layers (22) on the surface of the blade root (23), and high residual tensile stresses are found in the surface of the blade root (23), which could lead to crack propagation. Peening of the machined surfaces leaves compressive residual stresses near the surface and reduces the recast layers (22). The resulting blade root (23) meets the same specifications for durability and tolerances as a blade root machined using the conventional transfer line type cutting process, but at a fraction of the cost.

What is claimed is: 
     
       1. A method for producing turbine blade roots, comprising the steps of: (a) inputting data corresponding to a plurality of desired blade root shapes into an electro-discharge machining apparatus, storing the input data and selecting a desired blade root shape from the stored input data to be used to machine a blank turbine blade root;   (b) electro-discharge machining the blank turbine blade root into the desired blade root shaped; and   (c) peening the machined portion of the machined blade root at an intensity of from 4 almen to 6 almen to reduce surface recast and residual tensile stresses.   
     
     
       2. A method for producing turbine blade roots are recited in claim 1, wherein 110 steel shot is used for peening in step (c). 
     
     
       3. A method for producing turbine blade roots as recited in claim 1, wherein step (c) further comprises peening the machined portions with glass beads. 
     
     
       4. A method for producing turbine blades as recited in claim 1, wherein the machining in step (b) is done at a cutting speed of approximately 2.92 mm/min and a cutting current of 9 amps at 40 volts. 
     
     
       5. An apparatus for producing turbine blade roots comprising: means for electro-discharge machining a blank turbine blade root into a desired blade root shape and storing machining data;   means for inputting data corresponding to a plurality of blade root shapes into said electro-discharge machining means;   means for selecting the desired blade root shape from the stored input data to be used to machine the blank blade root; and   means for peening machined portions of the machined blade root at an intensity of from 4 almen to 6 almen for reducing surface recast and residual tensile stresses.   
     
     
       6. An apparatus for producing turbine blade roots according to claim 5, wherein 110 steel shot is used as peening material by said means for peening. 
     
     
       7. An apparatus for producing turbine blade roots according to claim 5, wherein glass beads are used as peening material by said means for peening. 
     
     
       8. An apparatus for producing turbine blades according to claim 5, wherein said means for electro-discharge machining operates at a cutting speed of approximately 2.92 mm/min and a cutting current of 9 amps at 40 volts.